This invention relates to a means and method for determining the condition of a surface with respect to ice, dryness, or water present at the surface. More particularly, it relates to systems for detecting icy, wet, and dry conditions on surfaces of aircraft, helicopter rotors, gasoline engine carburetors, roads, bridges, exposed structures, airport runways, taxiways, and refrigerator and freezer surfaces. The system can also be applied to surface condition monitoring of agricultural crops.
The presence, or absence, of ice at certain surfaces may be a fact of critical importance. The monitoring of ice and wetness on roads, bridges, airport surface, aircraft structures, and other surfaces necessarily exposed to atmospheric conditions is desirable.
Capacitance sensors for monitoring icing conditions have been proposed in the U.S. Pat. Nos. 3,428,890, 3,684,953, 3,873,927 and 3,882,381. All the above capacitance systems require bulky sensors which are not applicable for icing measurements under flow conditions, such as needed for aircraft applications. The system described in the U.S. Pat. Nos. 3,873,927, 3,882,381 requires complex interpretation of the measured variables and is, therefore, bulky, and expensive.
Thus it is seen that sensors for monitoring surface areas for testing the conditions of water for detecting icing conditions have been proposed with sensing elements of an undesirable size and shape and which are not amenable to positioning on a surface which is intended to receive currents of air flowing over the surface. These sizeable sensor elements among other undesirable attributes would interfere with the flow of air such as over the surface of an airplane wing or a helicopter rotor.
It will also be noted that other ice detecting systems which provide less obtrusive sensor electrodes employ means for interpreting the conditions and indicating icing which involve complex operations in providing notification of icing conditions. Such complex operations are unduly sensitive in performance and therefore unreliable in a procedure where reliability is of prime importance.
Other means such as mechanical vibration, air flow, and temperature testing sensors are even less reliable and encounter more interference.
Such monitoring systems encounter conditions which can hinder accurate and reliable operation of means for testing and identifying the presence or absence of water or ice.